A motion guide apparatus of this type is used to guide linear or curvilinear motion of a movable body. The motion guide apparatus includes a track rail extended in a longitudinal direction, a movable block movably assembled to the track rail via multiple rolling elements such as balls or rollers. A movable body is supported by the movable block. The rolling motion of the rolling element is used. Accordingly, it is possible to guide the motion of the movable body with high accuracy and obtain agile movements of the movable body.
In order to control the position of the movable body, it is necessary to measure the position of the movable body. In order to measure the position of the movable body, a scale is attached to the track rail, and a reading head that reads the scale is attached to the movable block or movable body. Scales are divided broadly into two types: an optical scale and a magnetic scale. The optical scale is a scale having a scale grating. A light emitting element and a light receiving device are used to detect a change in amount of light from the scale grating and output the amount of displacement. The magnetic scale is a scale having a fine magnetic pattern where the north and south poles are alternately arranged to detect the magnetic flux density of the magnetic pattern by a magnetometer such as a Hall sensor or a magnetoresistive element and output the amount of displacement.
The optical scale has an advantage that it is easy to increase measurement accuracy, but on the other hand, has a disadvantage that it is weak to contaminations such as dust and oil that block light. The magnetic scale has an advantage that it can be used even under an environment where there is dust, oil, or the like. In many cases, the motion guide apparatus is used under an environment where the advantage of the magnetic scale contributes largely. The magnetic scale is used for the motion guide apparatus in many cases.
As a motion guide apparatus where a magnetic scale is used, Patent Literature 1 discloses a motion guide apparatus that has a groove extended in a longitudinal direction in an upper surface of a track rail, a magnetic scale fitted into the groove, and a reading head attached to a movable block to read a magnetic pattern consisting of the north and south poles of the magnetic scale.